(a) Field of the Invention
The present invention relates to an electrode for electrolyzing an aqueous solution dissolving alkali metal chloride or any other electrolyte, and an ion exchange membrane electrolytic cell using a hydrogen generating cathode.
(b) Description of the Related Art
Electrolysis industry including chloroalkali electrolysis as its typical industry has an important role in material industry. In addition to this important role, energy-saving is earnestly required in a country where energy cost is high such as in Japan because the energy consumed in the chloroalkali electrolysis is higher.
The chloroalkali electrolysis has been converted from the mercury method into the ion exchange membrane method through the diaphragm method in order to solve the environmental problems and to achieve the energy-saving, and actually the energy-saving by about 40% has been attained in about 25 years. However, even the energy-saving to this extent is unsatisfactory, and as far as the current method is used, the further electric power saving is impossible while the cost of the energy or the electric power occupies about half of the total manufacture cost.
In an electrolytic cell mounting a hydrogen-generating cathode and used for brine electrolysis, cell voltage is reduced by disposing an anode, an ion exchange membrane and the hydrogen-generating cathode in intimate contact with one another. However, in a large-scaled electrolytic cell with an electrolytic area reaching to several square meters where an anode and a cathode are made of rigid materials, an inter-electrode distance can be hardly maintained at a specified value by intimately contacting both electrodes on an ion exchange membrane.
In order to reduce the interelectrode distance or a distance between the electrode and the corresponding electrode current collector or to maintain these at a nearly fixed value, an electrolytic cell using an elastic material therein is proposed.
The elastic material includes a non-rigid material such as a woven fabric, a non-woven fabric and a mesh, and a rigid material such as a blade spring.
The use of the non-rigid material arises such problems that the inter-electrode distance becomes non-uniform due to the partial deformation of the non-rigid material generated by the undue pressing from the counterelectrode side and the fine wires of the non-rigid material stick to an ion exchange membrane. The rigid material such as the blade spring inconveniently damages the ion exchange membrane, and reuse thereof may become impossible due to plastic deformation.
Various methods have been proposed for pressing the electrodes toward the ion exchange membrane in the ion exchange membrane electrolytic cell such as an electrolytic cell for brine electrolysis because the lowervoltage operation is desirable by intimately contacting the anode and the cathode with the ion exchange membrane.
As described, the structural characteristic of the electrolytic cell sandwiching the ion exchange membrane between the anode and the cathode is that, in order to prevent the damage of the ion exchange membrane by means of the uniform contact between the electrode and the ion exchange membrane and to maintain the inter-electrode distance to be minimum, at least one of the electrodes can freely move in a direction of the inter-electrode distance so that the electrode is pressed by an elastic element to adjust a holding pressure.
The elastic element includes a knitted fabric and a woven fabric made of metal wires or a structure prepared by stacking the fabrics, or by three-dimensionally knitting the fabrics or by three-dimensionally knitting the fabrics followed by crimp processing, and a non-woven fabric made of metal fibers, a coil hopper (spring) and a blade spring. These examples have spring elasticity of some kind.
On the other hand, the blade spring and the metal mesh are used for smoothly conducting the power supply from the current collector to the electrode in an industrial electrolytic cell such as that for brine electrolysis.
As described, however, the blade spring and the metal mesh are so rigid as to damage the ion exchange membrane and may not provide the sufficient electric connection due to its lower deformation rate.
In order to solve these problems, an electrolytic cell is disclosed in JP-B-63(1988)-53272 (FIGS. 1 to 8) in which a cathode is uniformly pressed toward a diaphragm to intimately contact the respective elements with one another by mounting a metal coil in place of the metal mesh between the cathode and the cathode end wall.
The extremely small diameter and the higher deformation rate of the metal coil sufficiently contact the respective elements with one another so that the stable operation of the electrolytic cell is possible.